The field of the invention relates to oscillators and more particularly to temperature controlled crystal oscillators.
Temperature controlled crystal oscillators (TCXOs) are generally known. Such devices are typically constructed in the form of a crystal and a controlling chip. Within the controlling chip, a set of switchable capacitors and a feedback amplifier form a tank circuit that oscillates at a frequency determined by the amount of capacitance switched into the tank circuit. By providing multiple capacitors that can be switched into and out of the tank circuit, the frequency at which the crystal oscillates can be varied. An internal power supply functions to drive the tank circuit at the predetermined frequency.
A temperature sensor is typically provided within the chip for sensing a temperature near the crystal. Based upon the temperature sensed, a controller switches capacitors into and out of the tank circuit based upon a performance criteria of the tank circuit. The performance criteria are typically stored in a lookup table within the TCXO chip.
However, consumers of TCXOs are demanding TCXOs with increasingly fast startup times while maintaining very low power consumption levels during ongoing operation.
During startup of the TCXO, however, the TCXO must execute numerous program instructions to begin oscillation of the crystal at the required frequency. Therefore, a CPU within the TCXO is required to operate at a high clock rate in order to accomplish this fast startup task. For example, during startup, a CPU of the TCXO must initialize, read a current temperature, retrieve operating characteristics at that temperature from a lookup table and program the operating parameters into the oscillator circuit within a very short time period (e.g., less than 1 ms).
The high clock rate of the CPU, however, greatly increases the power consumption of the TCXO. Therefore, a need exists for a TCXO that has a very fast startup time while maintaining low power consumption during ongoing operation.
As used herein, the term xe2x80x9cstartup timexe2x80x9d refers to the time interval between application of power to the TCXO and the instant when the TCXO reaches and maintains an operating frequency which conforms to its published operating parameters (e.g., 1 part per million frequency variation).
A method and apparatus are provided for reducing a startup interval of a temperature controlled crystal oscillator chip. The method includes the steps of connecting an operating circuit of the temperature controlled crystal oscillator chip into a first configuration to reduce the startup interval following application of power and reconnecting the operating circuit into a second configuration after a predetermined time period.